I was thinking about my airplane that has dual SV displays each with ADAHRS and each has a backup battery so I was under the assumption that there would be sufficient redundancy for IFR operations? My airplane has two independent electrical systems each powering its respective SV-1000 and a radio so when I designed the system it seemed to be way more robust than the old Piper airplanes with one electrical system and vacuum attitude and electric turn coordinator.
I have essentially the same thing (slightly modified Nuckolls Z-14, IIRC) in my COZY MKIV - two HDX's, two ADAHRS, no backup batteries since I have dual buses and dual alternators with a cross-tie. I agree that what you have is WAY better than a plane with a single electrical bus and vacuum instruments. I also put in a G5 as a non common mode susceptible standalone EFIS, in case SOMETHING manages to take out both ADAHRS's on the SV system. Extremely unlikely, but I already had the G5, so what the hell.
For the OP, either a 2nd ADAHRS or the standalone EFIS provide similar benefits, depending upon what the backup power schemes are. There are many ways to skin these cats.
What is your knowledge / experience with fiberglass airplanes and static electricity buildup/ discharge. A pilot in the Velocity community had a Garmin dual screen system and while climbing through a cloud layer both screens went blank but the airplane continued to fly normally on the autopilot and after climbing above the cloud the screens went back. He discussed it with Garmin and they downloaded the log and surmised that the cause was static electricity buildup/ discharge.
Fiberglass planes can have static buildup. They're not designed for lightning protection or isolation (at least the E-AB ones - Cirrus, et. al. do have some protection). I have a customer with a dual Garmin G3X system in his COZY MKIV and he has had substantial anomalous behavior while in IMC on a couple of occasions, which he attributed to static (also said that it felt like he was rubbing cats on his sweater at the same time that the screens were acting up).
If this indeed the case then I am curious about how to mitigate this risk with the SV-1000 and if I did install a third screen/ ADAHRS would the third device screen also go blank due to the same issue? The spinning gyros are more costly than a self contained unit.
While I have not heard of Dynon systems having issues with static buildup/discharge, I'd be surprised if they were substantially different than Garmin in that area. Maybe others on this forum can comment, particularly folks that fly a LOT of IMC. One of the advantages of an EFIS that isn't identical to the others (G5 with SV, AV-30 with SV, D10A with G3X, etc.) is the lack of many common mode failures due to different hardware and software design. And unless there's the same common mode failure with the backup EFIS, having a solid state device rather than a mechanical gyro is WAY more reliable.
My $0.02.
